Composite Body Lock Ring for a Borehole Plug with a Lower Slip Assembly

ABSTRACT

A borehole plug or packer for treating is designed to be milled out after use. The plug handles differential pressure from above using a lower slip assembly under a sealing element. A setting tool creates relative axial movement of a setting sleeve and a plug mandrel to compress the seal against the surrounding tubular and set the slips moving up a cone against the surrounding tubular to define the set position for the plug. The set position is held by a split lock ring having a wedge or triangular sectional shape and a surface treatment facing the mandrel that slides along the mandrel during setting movement but resists opposed reaction force from the compressed sealing element. The surface treatment can be a series of downhole oriented ridges such as a buttress thread that preferably penetrate the mandrel when holding the set position.

FIELD OF THE INVENTION

The field of the invention is borehole barriers and more particularly designs that see pressure from above and use materials the mill easily for removal after use and which lock in a set position for use.

BACKGROUND OF THE INVENTION

Borehole plugs are used in a variety of applications for zone isolation. In some applications the differential pressure experienced in the set position can come from opposed directions. These plug typically have a sealing element with mirror image slips above and below the sealing element. The plug is set with a setting tool that creates relative movement between a setting sleeve that is outside the mandrel and the plug mandrel. The slips have wickers oriented in opposed directions and ride out on cones to the surrounding tubular. The sealing element is axially compressed after the first set of slips bite followed by setting of the other set of slips on the opposite side of the sealing element from the first slip set to set. The set position of these elements is maintained by a body lock ring assembly. Body lock ring assemblies are in essence a ratchet device that allows relative movement in one direction and prevents relative movement in the opposite direction. The relative movement that compresses the sealing element and drives the opposed slips out on respective cones is locked by a body lock ring. Body lock rings are threaded inside and out and sit between tow relatively movable components. The thread forms are such that ratcheting in one direction only is enabled. A good view of such a design is shown in FIG. 13 of U.S. Pat. No. 7,080,693. The trouble with such a design in applications where the plug needs to be quickly milled out after use such as in treating or fracturing is that the shear loading on the ratcheting patterns is so high that the ratchet teeth break at loads that are well within the needed operating pressure range for the plug. With fracturing pressures going up and the use of readily milled components such as composites a new approach to locking was need and provided by the present invention. The goal is to hold the differential pressure from above while keeping the design simple so as not to prolong the milling time for ultimate removal. A typical zone treatment can involve multiple plugs that need to be removed. Elimination of upper slips when using the lock ring of the present invention also shortens milling time.

The lock ring is preferably split to ease its movement when axial opposed forces are applied to set the plug. The ring is tapered in cross section to allow it to act as a wedge against reaction force tending to relax the components from the set position. The side of the ring facing the mandrel has a surface treatment that provides minimal resistance in the setting direction and digs into the mandrel to resist reaction forces from the compressed sealing element in the set position. Preferably the surface treatment is a series of extending members oriented downhole with sharp ends that can dig into the mandrel for a firm grip. These and other aspects of the present invention can be better understood by those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.

Multicomponent body lock rings have been made of easily milled materials such as composites as illustrated in US 2014/0190685; U.S. Pat. No. 8,191,633; U.S. Pat. No. 6,167,963; U.S. Pat. No. 7,036,602; U.S. Pat. No. 8,002,030 and U.S. Pat. No. 7,389,823.

SUMMARY OF THE INVENTION

A borehole plug or packer for treating is designed to be milled out after use. The plug handles differential pressure from above using a lower slip assembly under a sealing element. A setting tool creates relative axial movement of a setting sleeve and a plug mandrel to compress the seal against the surrounding tubular and set the slips moving up a cone against the surrounding tubular to define the set position for the plug. The set position is held by a split lock ring having a wedge or triangular sectional shape and a surface treatment facing the mandrel that slides along the mandrel during setting movement but resists opposed reaction force from the compressed sealing element. The surface treatment can be a series of downhole oriented ridges such as a buttress thread that preferably penetrate the mandrel when holding the set position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of the plug in the run in position;

FIG. 2 is a close up view of the lock ring shown in FIG. 1 and

FIG. 3 is an exterior view of the plug.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 the plug or packer 10 has a mandrel 12 preferably made of a readily milled material such as a composite. Mandrel 12 can optionally have a passage 13 that can be optionally closed with a ball landed on a seat or with a valve (not shown). Shoulder 14 supports sealing element 16. A cone 18 has individualized tapered surfaces 20 on which a slip 22 is guided between opposed surfaces 24 and 26. The slips 22 are each connected to a slip ring 28 that has a triangular undercut 30 when viewed in section in FIG. 1 that extends for 360 degrees, preferably. The undercut is defined by surfaces 32 and 34 as better seen in FIG. 2. Lock ring 36 has an outer surface 38 that is preferably parallel to surface 32 of undercut 30. Bottom surface 40 of ring 36 is contacted by surface 34 of undercut 30 during the setting process. A shear pin or some other breakable member 42 allows the sealing element 16 to be compressed against a surrounding tubular that is not shown before the slips 22 are released to move up ramp surfaces 20 by the breaking of the shear pin 42. Movement of ring 28 relative to mandrel 12 brings together surfaces 34 and 40 to push the lock ring 36 in tandem with ring 28 during setting with a setting tool that is well known and is not shown and which serves as the force to brace the mandrel 12 while applying compressive force to the sealing element 16 and then extending the slips 22 against the surrounding tubular. The slips 22 have a surface treatment such as wickers 44 that resist reaction force from the compressed sealing element 16 as well as applied pressure loads from uphole applied in the direction of arrow 46.

The lock ring 36 has a surface treatment 48 on bottom surface 50 that faces the mandrel 12. During setting when the ring 28 takes lock ring 36 with it the surface treatment 48 rides along surface 54 of mandrel 12 without penetration of surface 54. However, after the set and release from the plug by the setting tool the reaction force from the sealing element 16 causes the downhole oriented ribs 56 to penetrate the surface of the mandrel 12 to brace the lock ring 36 so that it can act as a wedge using surface 38 to prevent motion of ring 28 in the direction of arrow 46.

Lock ring 36 can run continuously for nearly 360 with a single split to facilitate assembly to the mandrel 12. Alternatively, there can be discrete spaced segments for the majority of the 360 degree extent of the undercut 30. Undercut 30 can be continuous or discontinuous for 360 degrees to retain lock ring 36 when lock ring 36 is formed of discrete segments. The wedging action between surfaces 32 and 38 reduces the stress in an axial direction parallel to surface 54 to discourage shear failure of the ribs 56 while the preferred composite construction of the mandrel 12 encourages penetration through surface 54. The wedging action creates a radial and axial component forces to the ribs 56 to increase the penetration into the mandrel 12 and to decrease the axial shear force component acting on the ribs 56 at the outer surface of said mandrel 12. The ribs 56 can be parallel or one or more spiral patterns or a thread form such as a buttress thread. The rib spacing can be equal or variable. The lock ring 36 can preferably be made of composite material or a soft metallic that can be easily drilled. Optionally, if lock ring 36 is a continuous split ring the faces 58 and 60 that define the split can be placed on opposed sides of a tab 62 on mandrel 12 to rotationally lock the two together to prevent lock ring relative rotation with respect to the mandrel 12 when milling out. When segments are used for the lock ring 36 each segment can be rotationally retained in a dedicated undercut 30 in ring 28 to rotationally secure the components when milling out. Alternatively, some or all of the above described plug 10 apart from sealing element 16 can be made of a disintegrating controlled electrolytic material to forgo the milling out altogether.

Optionally the ribs 56 can be omitted so that bottom surface 50 can make frictional contact with surface 54 with no or minimal penetration so that the retaining force is principally or entirely a frictional contact. Surface 50 can have surface roughening or it can even be smooth. While the ability to hold reaction force may be somewhat decreased without the ribs 50 there is still enough resistance to reaction force to hold the set position for some applications. Wedging action creates the frictional retention force.

The teachings of the present disclosure may be used in a variety of well operations. These operations may involve using one or more treatment agents to treat a formation, the fluids resident in a formation, a wellbore, and/or equipment in the wellbore, such as production tubing. The treatment agents may be in the form of liquids, gases, solids, semi-solids, and mixtures thereof. Illustrative treatment agents include, but are not limited to, fracturing fluids, acids, steam, water, brine, anti-corrosion agents, cement, permeability modifiers, drilling muds, emulsifiers, demulsifiers, tracers, flow improvers etc. Illustrative well operations include, but are not limited to, hydraulic fracturing, stimulation, tracer injection, cleaning, acidizing, steam injection, water flooding, cementing, etc.

The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: 

1. A plug or packer assembly for borehole use, comprising: a mandrel supporting a sealing element and a retaining member disposed between said sealing element and one of opposed ends of said mandrel; a lock ring having a surface treatment facing said mandrel, said surface treatment oriented toward a second of said ends of said mandrel, said surface treatment configured for sliding contact with an outer surface of said mandrel when moving toward a first of said ends for setting said sealing element and said retaining member and said surface treatment configured to penetrate said outer surface of said mandrel when moving toward said second end.
 2. The assembly of claim 1, wherein: said lock ring comprising a tapered surface opposite said surface treatment.
 3. The assembly of claim 1, wherein: said lock ring comprises a split ring.
 4. The assembly of claim 1, wherein: said lock ring comprises spaced segments.
 5. The assembly of claim 1, wherein: said lock ring is rotationally locked to said mandrel.
 6. The assembly of claim 1, wherein: said surface treatment comprises a plurality of ribs oriented toward said second end, said second end oriented downhole from said first end.
 7. The assembly of claim 6, wherein: said ribs are parallel.
 8. The assembly of claim 6, wherein: said ribs comprise a spiral.
 9. The assembly of claim 6, wherein: said ribs comprise a thread form.
 10. The assembly of claim 6, wherein: said ribs are evenly or unevenly spaced.
 11. The assembly of claim 1, wherein: said lock ring comprises a triangle shape in section.
 12. The assembly of claim 11, wherein: said retaining member comprises slips; said slips are retained to said mandrel by a slip retainer ring defining at least one undercut conforming to the shape of said lock ring.
 13. The assembly of claim 12, wherein: said undercut and lock ring comprise aligned tapered surfaces with respect to said outer surface of said mandrel such that movement of said slip retainer ring against said lock ring in response to a reaction force from a set said sealing element pushes said surface treatment to penetrate said outer surface of said mandrel.
 14. The assembly of claim 13, wherein: said tapered surfaces apply a radial and axial component forces to said surface treatment.
 15. The assembly of claim 14, wherein: said surface treatment comprises a plurality of ribs oriented toward said second end, said second end oriented downhole from said first end.
 16. The assembly of claim 15, wherein: said ribs are parallel.
 17. The assembly of claim 15, wherein: said ribs comprise a spiral.
 18. The assembly of claim 15, wherein: said ribs comprise a thread form.
 19. The assembly of claim 15, wherein: said ribs are evenly or unevenly spaced.
 20. A treatment method for borehole use, comprising running in a packer or plug mandrel supporting a sealing element and a retaining member disposed between said sealing element and one of opposed ends of said mandrel and a lock ring having a surface treatment facing said mandrel, said surface treatment oriented toward a second of said ends of said mandrel, said surface treatment configured for sliding contact with an outer surface of said mandrel when moving toward a first of said ends for setting said sealing element and said retaining member and said surface treatment configured to penetrate said outer surface of said mandrel when moving toward said second end; setting said sealing element and retaining member; pumping a treatment into the borehole against said packer or plug.
 21. A plug or packer assembly for borehole use, comprising: a mandrel supporting a sealing element and a retaining member disposed between said sealing element and one of opposed ends of said mandrel; a lock ring facing said mandrel, comprising a surface configured for sliding contact with an outer surface of said mandrel when moving toward a first of said ends for setting said sealing element and said retaining member and said surface configured to frictionally engage using wedging action said outer surface of said mandrel when moving toward said second end.
 22. A treatment method for borehole use, comprising running in a packer or plug mandrel supporting a sealing element and a retaining member disposed between said sealing element and one of opposed ends of said mandrel and a lock ring facing said mandrel, comprising a surface configured for sliding contact with an outer surface of said mandrel when moving toward a first of said ends for setting said sealing element and said retaining member and said surface configured to frictionally engage using wedging action said outer surface of said mandrel when moving toward said second end setting said sealing element and retaining member; pumping a treatment into the borehole against said packer or plug. 